Metalloprotein metal sites will be characterized by an application of various physical techniques on both selected metalloproteins and model systems. The specific proteins under study are putidaredoxin, P450, chloroperoxidase and mushroom tyrosinase. Variable-temperature magnetic susceptibility, photoelectron spectroscopy, Fe57 Mossbauer, esr, polarography and variable-temperature infrared spectroscopy are the techniques being used. Model systems for the mixed-valence character of the ferredoxins are being investigated with the intention of determining whether electron exchange interaction between nearby iron centers is the dominant factor determining the rate of intervalence transfer. The high-spin low-spin phenomenon is being studied with variable-temperature (20-300 degrees K) infrared spectroscopy. A characterization of the copper site(s) in mushroom tyrosinase continues to develop. The denaturing process for this cuproprotein is being studied in conjunction with studies of the effects of substrate modification.